High-pressure sheets used as gasketing material have traditionally been prepared by mixing a base of fibers with a rubber binder and subjecting the resultant mixture to pressure and elevated temperature. The standard process for manufacturing high pressure sheets has involved mixing two separate component doughs, both of which have been essential components in making the high pressure sheet product. The main component, referred to as the body dough, has been mixed, for example, in a large drum mixer, although it has been known to be mixed in any of a variety of different mixer types. The components of this dough have typically included, for example, elastomers such as rubber materials, fibers, fillers such as clay, and small quantities of other materials, such as curing components, antioxidants and/or coloring agents which are known to those skilled in rubber compounding technology.
Typically, high-pressure sheets have been made on a two-roll sheeter machine, such as a Troester machine, which has a pair of rolls, one positioned above the other. The lower roll has been typically provided as a larger, heated roll while the upper roll has been provided as a smaller, normally unheated roll. To the conventional sheet on a machine of this type, a quantity of starter compound is first built up on the hot roll. A quantity of body compound is then added in the nip between the two rotating rolls. A high pressure sheet material is formed on the hot roll to the desired thickness and can then be removed and placed on a table or other support.
The high-pressure sheets have been used to form gaskets that may be placed between flanges, for example, of a conduit connection to provide a seal between the faces of the flanges. The typical gasketing material has been formed with a fairly small amount of rubber binder, on the order of 10-15% by weight, a quantity of clay which functions primarily as a filler, on the order of 20% or less, and a quantity of fibers to hold the material together. Compressed sheet gasketing materials have generally provided a secure seal against fluids, but only when used with flanges that are in good condition and when sufficient pressure has been applied to ensure a complete seal. A disadvantage of prior sheet gasketing materials has been the fact that a relatively large clamping force has been required to provide an adequate seal. However, such sheet gasketing materials have not been typically strong enough to withstand the required clamping pressure.
Sheet gasketing materials containing about 20% bentonite in the formulation have been known to swell in oils, thus providing a seal in applications such as pumps and engines. However, they have not been shown to provide an enhanced seal in water. In addition, while some sheet gasketing materials have provided an excellent seal when infused with a swelling medium such as oil or water, operations with frequent cycles of startup and shutdowns can been shown to inhibit the performance gains associated with highly swellable sheet formulations. Accordingly, there is a present need for an improved compressed sheet gasketing material which is particularly adapted to operate effectively in oil and water media, as well as when the process line is dry.